Tetracyclines (TCs), including tetracycline (TTC), oxytetracycline (OTC), and chlorotetracycline (CTC), are frequently detected in natural waters, soils, and sediments, which raised great concerns about the proliferation of antibiotic resistant genes. This study investigated the degradation of TCs by sulfate radical produced by thermo-activated persulfate in aqueous solution. Increasing the temperature significantly enhanced the degradation of TTC, and the relationship between pseudo-first-order rate constant (k obs) and temperature obeyed Arrhenius equation. The degradation of TTC showed pH dependency, and k obs increased markedly with increasing pH. Seven intermediate products of TTC were temporarily identified by solid phase extraction and liquid chromatography-tandem mass spectrometry (SPE-LC-MS/MS). The transformation pathways of TTC included N-demethylation, hydroxylation-oxidation and dehydration. Detailed mechanisms for sulfate radical-induced N-demethylation and hydroxylation-oxidation were proposed. The degradation of the three TCs followed the order of OTC ＞ CTC ＞ TTC, highlighting the structure-specific reactivity. Interestingly, TTC was degraded extremely fast in artificial surface water (ASW), implying sulfate radical-based oxidation of TCs may be efficient in

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Persulfate (PS) is widely used as an oxidant for in situ chemical remediation of contaminated groundwater. In this study we demonstrated for the first time that PS could be activated by bicarbonate. Acetaminophen was used as the probe compound to examine the reactivity of PS/bicarbonate system. It was found that acetaminophen could be effectively transformed and the reaction rate appeared pseudo-first-order to the concentrations of both acetaminophen and PS. Radical scavenger tests indicated that neither free radicals (SO and HO) nor superoxide (O) was responsible for acetaminophen transformation. Generation of singlet oxygen (O) was verified using furfuryl alcohol (FFA) as a probe. Formation of O was further quantified in DO fortified solution based on kinetic solvent isotopic effect (KSIE) but it was found that O contributed only 51.4% of the total FFA transformation. The other 48.6% was presumed to be ascribed to the reaction with peroxymonocarbonate (HCO). However, the transformation of acetaminophen was mostly due to the reaction with HCO but not O. Instead of degradation, HCO oxidized acetaminophen via a one-electron abstraction mechanism resulting in the generation of acetaminophen radicals which coupled to each other to form dimers and trimers. HCO also hydrolyzed rapidly to form hydrogen peroxide (HO) which led to the formation of O, during which O was a key intermediates. Because bicarbonate is ubiquitously presented in groundwater, the findings of this research provide important insights into the fundamental processes involved in PS oxidation in subsurface.

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Sulfaquinoxaline (SQX) is a coccidiostatic drug widely used in poultry and swine production and has been frequently detected in various environmental compartments such as surface water, groundwater, soils, and sediments. In the present study, degradation of SQX by ferrous ion-activated peroxymonosulfate oxidation process (Fe(II)/PMS), a promising in situ chemical oxidation (ISCO) technique, was systematically investigated. Experimental results showed that Fe(II)/PMS process appeared to be more efficient for SQX removal relative to Fe(II)/persulfate process (Fe(II)/PS). An optimal Fe(II):PMS molar ratio of 1:1 was found to be necessary for efficient removal of SQX. Increasing the solution pH hampered the degradation of SQX, and no enhancement in SQX degradation was observed when chelating agents S,S'-ethylenediamine-N,N'-disuccinic acid (EDDS) and citrate were present. The presence of Suwannee River fulvic acid (SRFA), as a representative of aquatic natural organic matter (NOM), could inhibit the degradation of SQX. SQX was more susceptible to Fe(II)/PMS oxidation in comparison to its substructural analog 2-amino-quinoxaline (2-AQ) and other sulfonamides, i.e., sulfapyridine (SPD) and sulfadiazine (SDZ). Transformation products of SQX were enriched by solid-phase extraction (SPE) and identified by liquid chromatography-electrospray ionization-triple quadrupole mass spectrometry (LC-ESI-MS/MS). On the basis of the TPs identified, detailed reaction pathways for SQX degradation including sulfonamide bond cleavage, SO extrusion, and aniline moiety oxidation were proposed. Our contribution may provide some useful information for better understanding the kinetics and mechanisms of SQX degradation by sulfate radical-based advanced oxidation processes (SR-AOPs).